Overlapping blow ring for filters



ZENSW QVERLAPPING BLOW RING FOR FILTERS 2 Sheets-Sheet 1 Filed May 11, 1948 gin lm ig l Eda awe 2W4 159 w. M. a -Hzwcm OVERLAPPING BLOW RING FOR FILTERS Filed May 11, 1948 2 Sheets-Sheet 2 IN V EN TOR.

Patented June 13, 1950 OVERLAPPING BLOW RING FOR FILTERS William M. Sheldon, Elizabeth, N. J asslgnor to Pulverizing Machinery Company, Summit, N. .l., a corporation of New Jersey Application May 11, 1948, Serial No. 26,334

4 Claims. 1

This invention relates to self-cleaning dust filters of the type in which the filter itself is a vertical tube or cylindrical bag of felt or closely woven fabric. The dust-laden gas, usually air, is introduced into the interior of the filter tube adjacent its upper end and the dust-free air escapes outwardly through the interstices of the felt, leaving a layer of dust on the inner surface of the tube. This layer, together with any dust which is caught in the interstices of the felt, is removed by blowing relatively high pressure air from a ring surrounding the tube through the felt from the outside. This ring has a slot around its inner periphery for the discharge of such high pressure air. To insure that the air issuing from the slot passes through the felt, the inner diameter of the cleaning air or blow ring is made less than the outer diameter of the tube when distended. The ring is reciprocated slowly up and down the filter bag so as to clean successively the whole bag. The air passing from the blow ring through the felt into the interior of the filter tube eventually escapes outwardly through the portions of the felt not in contact with the ring.

It has been found that it is highly important to get the right proportion between the diameter of the tube and that of the ring. If the diameters are too nearly the same, there is leakage of air between the outside of the filter tube and the ring. If the diameter of the tube is too large with respect to that of the ring, the tube is wrinkled and fluted around its entire periphery in the neighborhood of the ring, permitting escape of cleaning air at the fluted portions. Also wear on the tube is increased unnecessarily.

The felt filter tubes vary in diameter considerably. This is partly the result of the practical difiicultv of sewing together a sheet of felt into cylindrical form to give a. tube of exactly the desired diameter. Then again. the felt bag stretches or contracts with variations in humidity. Wear also changes the dimensions of the bag. For these reasons the ring has been made discontinuous with its ends separated so that, by increasing or decreasing such separation, the inner diameter of the ring could be increased or decreased proportionately.

Tbe se aration of the ends of the blow-ring leaves a gap permitting a convex vertical flute to form in. the felt as the latter is pushed outwardly by the internal air pressure into such gap. This is apt to produce excessive wear along the vertical section of the filter bag registering with such gap. This is particularly the case when the filter is assembled so that its longitudinal seam registers with the gap.

The object of the present invention is to provide a blow ring whose internal diameter can be varied without presenting a gap into which the filter tube can be pushed outwardly.

According to the present invention, therefore, the ring is helical in form with at least its end portions overlapping. By varying the degree of overlap, it is possible to change the inner circumference of the ring.

The blow ring may be made to contact the felt tube for one turn or 360 or more, or for two turns or 720 more or less.

The latter construction is advantageous as it enables a more thorough application of the cleaning air than a one-turn ring. The slot in the blow ring is ordinarily not continuous but is made up of a series of slots separated from each other by /8" to bridge of metal. That is desirable to keep the width of the slot constant. The usual mode of making the blow rings is to bend them into circular form and then mill out the slots. The bending produces internal strains and stresses and, even if the ring were annealed after bending and before milling the slots, the expansion or contraction of the ring to make it fit the felt tube properly would produce strains and stresses which would change the width of the slot. Bridges at frequent intervals keep the slot width constant.

The felt opposite these intervening bridges does not receive its proper supply of cleaning air. With a two-turn ring these discontinuous slots may be staggered so that the intervening bridges in the two turns do not register with each other.

Two suitable forms of construction are illustrated. by way of example, in the accompanying drawings, wherein:

Fig. 1 is a side elevation of a filter embodying the improved type of blow ring;

Fig. is a p an view of the blow rin Fig. 3 is a side elevation of the blow ring;

Fi 4 is a section on the line 4-4 of Fig. 1;

Fig. 5 is a section on the line 5-5 of Fig. 3;

Fig. 6 is a side elevation of a modified form of blow ring; and

Pig. 7 is a section on the line I--1 of Fig. 6.

The filter comprises a tube In of suitable filterinr; material, preferably felt, attached at its upper end to a downwardly extending flange on a circular closure I l. This closure is hung from a platform I! by bolts I3. This platform, in ilngrn, is suspended from the floor above by bolts The lower end of the tube I is secured to the top of a hopper l1, terminating in a discharge spout Ill. The bag is held taut in a vertical directlon by providing springs is between the heads of bolts l3 and the platform I 2.

Dust-laden air is introduced into the interior of the filter tube by a blower 20 having an intake pipe 2i and a discharge pipe 22. The latter, by means of elbow 23 and vertical extension 24, carries the dust-laden air into the upper part of the filter tube, so that the incoming air with a low dust concentration is not mixed with the air in the lower part of the tube having a very high dust concentration. The air so introduced escapes outwardly through the pores of the filter leaving the dust behind on the inner surface of the filter and to some extent in the interstices in the superficial portions of the filter material. Unless such dust is periodically removed, the flow of air will get less and less and the pressure required to force it through the filter will progressively increase.

Removal of dust is accomplished by reversal of air fiow. For this purpose a cleaning air or blow ring 25 is provided having an internal diameter slightly less than the external diameter of the filter tube when distended by the pressure of the dust-laden air. Along its inner periphery this ring has a series of slots 26 for the discharge of the relatlvelyhigh pressure cleaning air. This air is supplied through a flexible hose 2] from anair-pump 28 driven by motor 29.

The blow ring is reciprocated up and down the filter tube by means of two chains 32 arranged on diametrically opposite sides of the filter tube. These chains pass over pairs of sprocket wheels 33 and 34. The sprockets 33 are driven continuously in unison through a worm reduction gear by motor 28.

The blow tube is connected to each chain 32 by two chain lengths 36 and 31, each connected at one end to a pin 38 on the blow ring and at their other ends to pins 39 and 40 projecting laterally from the sprocket chain. These chain lengths 3B and 31 are longer than the diameter of the sprocket wheels 33 so that, at the end of the upward movement of the blow ring, when the pins 39 and 40 pass over the tops of the sprocket wheels 33, the pins 38 are below the bottoms of such sprockets.

At the end of its downward movement, the blow ring rests on the top of the hopper i l before the pins 38 strike the sprockets 34.

One of the most important features of the invention is the operative relationship between the blow ring and the filter bag. As shown in Fig. 1, it will be noted that as the internal diameter of the ring is less than the external diameter of the filter tube when distended, the ring produoes a concavo-convex portion in the felt as shown in detail in Fig. 4.

This has two important effects. First, it prevents the high pressure cleaning air escaping laterally without going through the felt and performing its cleaning function. Another important effect is that the bending of the felt into concavo-convex form tends to open up the interstices on the inner wall of the filter as well as crack ofi the layerof dust deposited on the inner surface of the felt. This bending and resulting opening of the pores in thefelt greatly aids the cleaning of the filter.

If the ring is too small in diameter, it produces longitudinal creasing or fiuting of the filter tube all around its periphery. This interferes with proper contact between the ring and the filter tube as well as increasing wear unnecessarily. If the ring is too large, much of the cleaning air will escape laterally and the bending of the felt will be too slight to give really good results.

To enable the circumference of the blow ring to be adjusted to suit the dimensions of the particular filter tube with which it cooperates, the blow ring is made helical in form with at least its end portions overlapping.

In the form of construction shown in Figs. 1 to 5, inclusive, only the ends overlap. To the lower of the two ends a bracket 45 is welded or soldered. This bracket extends first upwardly and then laterally, To the upper of the two ends is welded or soldered another bracket 46 having one arm extending laterally and another arm projecting downwardly. A bolt 49 extending through the vertical portions of both brackets enables the overlapping ends of the ring to be drawn over each other to the extent necessary to give the ring its desired diameter. The two laterally extending portions of the two lugs are in sliding relation to each other. A bolt 41 passing through a hole in bracket 46 and a slot 48 in bracket 45 holds the two brackets and the ring ends to which they are attached in proper relative vertical position.

One end of the ring is provided with a closure fill. The other end of the ring is coupled to the flexible hose 21.

The slots 26 are, as shown, discontinuous so that as the ring is drawn together to reduce its diameter, the width of the slots will not be changed substantially.

The felt opposite the bridges intervening between the slots does not receive its proper supply of cleaning air. Even when these bridges are short it may be found more efiicient to use a two-turn ring, as shown inFig. 6, to permit the slots in one turn to be staggered so that the in tervening bridges in the two turns do not register with each other.

The bracket 5| is secured to the ring near its lower end while the bracket 52 is attached to the ring near its upper end. There is no connection between. either bracket and the middle section of the ring. The drawing of the ends together causes substantially uniform distortion of the ring throughout its entire length.

The bolts 54 and 55 function in exactly the same manner as the corresponding bolts 41 and 49 in the one-turn construction of Figs. 1 to 5, inclusive.

I claim:

1. A self-cleaning dust filter of the type having a circular cleaning-air ring adapted to be reciprocated up and down the outside of a vertical filter tube, the inner diameter of the ring being less than the outer diameter of the tube when distended, in which the cleaning-air ring makes two helical turns around the filter tube and both turns are provided with a series of slots separated. by bridges around their inner peripheries for the esca e of air, the slots in one turn being staggered with respect to those in the other turn so that the bridges in the two turns do not register with each other.

2. A self-cleaning dust filter of the type having a circular cleaning-air ring adapted to be reciprocated up and down the outside of a vertical filter tube, the inner diameter of the ring being less than the outer diameter of the tube when distended, in which the ring is formed of a single tube bent into helical form with at least its end portions overlapping, projections on the end portions of the ring and means for changing the distance between said projections to vary the degree of overlap of such end portions to change the inner circumference of the ring.

3. A self-cleaning dust filter of the type having a circular cleaning-air ring adapted to be reciprocated up and down the outside of a vertical filter tube, the inner diameter of the ring being less than the outer diameter of the tube when distended, in which the ring is formed of a single tube bent into helical form with at least its end portions overlapping and is provided with a series of slots separated by bridges around its inner periphery for the escape of air, projections on the end portions of the ring and means for changing the distance between said projections to vary the degree of overlap of such end portions to change the inner circumference of the ring.

4. A self-cleaning dust filter of the type having a circular cleaning-air ring adapted to be reciprocated up and down the outside of a vertical filter tube, the inner diameter of the ring being less than the outer diameter of the tube when distended, in which the ring is formed of a single tube bent into helical form with at least two REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,321,490 Sweetland Nov. 11, 1919 1,944,268 Rathbun Jan. 23, 1934 2,476,942 Arnold July 19, 1949 2,495,635 Hersey Jan. 24, 1950 FOREIGN PATENTS Number Country Date 709,109 Germany Jan. 20, 1940 737,109 Germany July 7, 1943 

